Field of the Invention
Aspects of the present invention relate to an oscillation device and a measurement apparatus using the same.
Description of the Related Art
A terahertz wave is an electromagnetic wave in a frequency range from a millimeter wave band to a terahertz band (30 GHz to 30 THz). Regarding many organic molecules of biomaterials, medical supplies, electronic industry materials, and the like, absorption peaks due to a structure or a state exist in the frequency range of the terahertz wave. The terahertz wave passes well through materials, such as paper, ceramic, resin and cloth. An imaging technique and a sensing technique utilizing the property of the terahertz wave are being researched and developed recently.
For example, these techniques are expected to be applied to a safe fluoroscopic inspection apparatus that replaces an X-ray apparatus, and to an in-line nondestructive inspection apparatus in a manufacturing process.
An exemplary oscillation device that oscillates the terahertz wave includes a current injection type oscillation device using an electromagnetic gain based on transition of electrons between subbands in a semiconductor quantum well structure. A quantum cascade laser (QCL) in a terahertz wave band in which a double-side metal waveguide (DMW) known as a low-loss waveguide structure is integrated as a resonator or, a resonant tunneling diode (RTD) is proposed. Such an oscillation device has a waveguide structure in which metals are disposed upper and lower sides of an about 10 μm thick gain medium of a semiconductor film. The oscillation device guides a terahertz wave generated by stimulated emission to the waveguide structure in a surface plasmon mode to cause resonance. With this configuration, laser oscillation near 3 THz is achieved by high optical confinement and low-loss propagation.
As a method of extracting an electromagnetic wave from a waveguide structure, U.S. Patent Application No. 2012/0134380 proposes a method of disposing a low reflective film on an end surface of the waveguide structure to improve extraction efficiency. U.S. Patent Application No. 2016/0006215 discloses a structure in which a patch antenna is provided on an end surface of a waveguide structure which has a RTD in an active layer.